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  • Author or Editor: Dave P. Loparco x
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All current onion cultivars are susceptible to Botrytis squamosa (BLB), in varying degrees. The wild onion relative Allium roylei possesses strong BLB resistance. To control this disease, BLB resistant onion populations are being created through backcross breeding using A. roylei. Interspecific sexual barriers reduce fertility and seed set, impeding gene transfer. It is relatively easy to make the interspecific F1 between A. roylei and Alliumcepa; however, sexual barriers severely limit seed production in subsequent generations. Nevertheless, we were able to select BC1F2 plants capable of generating high levels of BC2F1 seed. The BC2F1 plants had horticultural characteristics much closer to onion, and segregated for both BLB resistance and fecundity. One particular BC2F1 population gave the highest proportion of resistant plants in a field screen, and nearly all plants of this population produced true bulbs. 120 selected BC2F1 bulbs were retested for BLB resistance in a chamber assay and the most resistant plants were used to advance the transfer of BLB resistance. In 2004, BC2F2 and BC3F1 populations derived from the BC2F1 selections were screened for BLB resistance and used for seed production. 132 plants were selected in the field screen. The level of resistance in BC2F2 and BC3F1 is similar to BC1F2 and BC2F1, with no evidence of reduction in level of resistance with generations. Molecular screens for markers associated with resistance are routinely used in vegetable crops to transfer resistance genes. The creation of a molecular assay for BLB resistance would accelerate its transfer and release of resistant varieties. We are using AFLP and SSRs in a search for DNA markers associated with BLB resistance in our materials.

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